The aim of this study is to develop a method of automating cytologic examinations of the urinary bladder to detect, diagnose and evaluate carcinoma and precancerous lesions. In prior studies, cells in suspension were fluorescing dyes for DNA and RNA, and measured by flow cytometry at rates of several hundred cells per second. The tumors with aneuploid stemlines were readily diagnosed. In preliminary studies these accounted for 90% or more carcinomas and carcinomas in situ. Papillomas differed from normal by high proliferative cell fractions, but few had aneuploid stemlines and high proliferative cell fractions were seen also with severe cystitis. We now intend to develop a flow cytometry feature based on chromatin structure to increase the accuracy of diagnosis of tumors without well-defined aneuploid stemlines. These are several possible approaches that are quite promising: DNA intercalating probes (or nucleases) of differing size or affinity that demonstrate differences in accessibility of DNA in chromatin; combinations of dyes that compete for the same DNA binding sites, or that have different specifities in binding; energy transfer between dye pairs; changes in fluorescence polarization of DNA-bound fluorescent probes; or differences in resistance to thermal or acid denaturation. At the same time we intend to continue long term detailed clinicopathologic correlation of flow cytometry findings on the large population of urologic patients at Memorial Sloan-Kettering Cancer Center. These studies are necessary to define the potential clinical applications of flow ctyometry in the detection of bladder cancer and precancerous lesions, in tumor grading and assessing proliferative rates and extent of mucosal involvement, and in monitoring the effects of treatment.